1. Field of the Invention
This invention relates to a method for separating a color region from an image. This invention particularly relates to a method for separating a color region, which is constituted of same-color components in a color image, from the color image.
2. Description of the Prior Art
There have heretofore been proposed various methods for extracting a face pattern region from an image, in which the face pattern is embedded, or for recognizing whether an extracted region is or is not a face pattern. For example, a method for recognizing a face pattern in a color image is proposed in"Face Position Matching Method Using Color Information for Face Image Recognition" by Sasaki, Akamatsu, and Suenaga, Singiho, IE91-2, 1989. With the proposed method, a color image is converted to the YIQ base or the HVS base, and a region of flesh color, which is the color of a face, in the image is taken as a face pattern region. Also, reference points are set at eye patterns, a mouth pattern, and the like, in the face pattern region, and the face pattern is recognized from the relationship among the reference points.
Also, neural networks using a line process, which is an early vision model, has been proposed in, for example,"Neuroral Networks in Early Vision" by C. Koch, J. Marroquin, and A. Yuiie, Anaklog, Proc. Natl. Acad. Sci. U.S.A., Vol. 83, pp. 4263-4267, June 1986. With the neural networks using the line process, without high-level knowledge being used, a function, which is referred to as the line process and represents the presence or absence of discontinuity between a continuous value and an adjacent continuous value, is applied to neural networks, and an energy function for estimating a situation of the maximum posterior probability is obtained. Also, the minimum value of energy is calculated, and the presence or absence of continuity or discontinuity of a distribution of certain values is detected.
Further, an image processing apparatus utilizing the method with the line process of Koch, et al. has been proposed in, for example, Japanese Unexamined Patent Publication No. 3(1991)-99379. In the proposed image processing apparatus, a plurality of local area limited probability fields, which have different levels of resolution, and information representing the positions and shapes of feature points are located in a layer pattern, and interactions between the respective layers is utilized. In this manner, the proposed image processing apparatus is provided with a function for restoring an image having good image quality and a contour line extracting function, which reflect general information.
Specifically, in the proposed image processing apparatus, a plurality of layers are located, which extract a plurality of the local area limited probability fields, that have different levels of resolution, and information representing the positions and shapes of the feature points. Also, interactions between a many-valued stochastic variable, which represents the gray level values of the image, and a binary stochastic variable, which represents the presence or absence of discontinuity of the gray level values in the image, are utilized. Image processing is carried out by using general information between the respective layers. In this manner, image processing, such as restoration of an image having good image quality and contour line extraction, is carried out such that the general information may be reflected.
Furthermore, a method for extracting a contour line in an image by using the line process has been proposed in, for example,"Contour Line Extraction with a Local Parallel Probability Algorithm Having an Energy Learning Function" by Hongo, Kawahito, et al., Collected Papers of The Institute of Electronics and Communication Engineers of Japan, D-II, Vol. J74-D-II, No. 3, pp. 348-356, March 1991. With the proposed method, the technique using the line process, which is proposed by Koch, et al., is utilized for a black-and-white image, in which a face pattern is embedded. Specifically, an energy function is used, which is defined by density values of the image and the line process representing the presence or absence of continuity of the density values. A calculation is made to find the minimum value of energy, which is represented by the energy function, and a contour of the face pattern embedded in the black-and-white image is thereby extracted. This technique is characterized by an energy learning function for determining the parameters of the energy function through learning operations.
However, the method proposed by Sasaki, et al. is applicable only to limited kinds of images, in which no background is present, a face pattern is located in the vicinity of the center point of the image, and no spectacle pattern is present. Thus with the proposed method, a face pattern cannot be recognized or extracted regardless of the kind of image.
Also, the method proposed by Koch, et al., the method described in Japanese Unexamined Patent Publication No. 3(1991)-99379, and the method proposed by Hongo, et al. are applicable only to the extraction of a face contour from a gray level image. The proposed methods have the drawbacks in that, in cases where they are used for an image having a background or an image having a pattern of color similar to the face color around the face pattern, the background or the pattern around the face pattern becomes amalgamated with the contour of the face pattern, and the contour of the face pattern does not close. Therefore, with the proposed methods, the face pattern cannot be separated accurately from the image.